In the fixing devices used for image forming apparatuses such as electrophotographic copying machines and printers, rollers and belts with low heat capacity are often used as fixing members for heating and/or pressurizing conveyed sheets in order to reduce a warming up time. Although use of such rollers and belts with low heat capacity achieves quick temperature increase, heat transfer becomes difficult in the longitudinal direction of the rollers (width direction of the belts). Accordingly, heat pipes, which are made by enclosing operating fluid (such as water) in the pipes made of metal with sufficient heat conduction (such as copper and aluminum), are placed as heat equalizing members along the rollers and the belts, and are brought into pressure contact therewith. As a consequence, the latent heat of the operating fluid enclosed in the heat pipes is used to reduce temperature distribution difference in the longitudinal direction of the rollers (width direction of the belts), by which heat equalization is achieved.